The present invention relates to a novel and improved flexible drive cable, and more particularly to a flexible drive cable in use for transmitting power with a rotary motion in motor vehicles.
Flexible drive cables have been used in a variety of applications where it is desirable to transmit rotary motion or torque to speedometers, tachometers, and the like, remote from the wheel section in motor vehicles.
Flexible drive cables of such a type need to sufficiently fulfill the requirement of silence upon operation thereof in order to meet the demand in the recent years of requesting a silent motorcar, in addition to another essential requirements such as of strength and durability to drive speedometers for a long period of time as well as of suitable flexibility so as to connect the speedometers with the wheel section (generally not axially aligned) therethrough.
Upon operation of the flexible drive cable, it has been observed that the severe oscillation of the core member arises often due to unavoidable uneven torque distribution therealong, which oscillation causes the core member to indiscriminately impinge against the interior face of the liner member, and thereby produces a noise. The noise thus produced is propagated outside through the outer member. The oscillation is also transferred to the dash-board or the like in motorcars through the outer member to result in causing a resonance therewith and thereby amplyfied, which is extremely undesirable for the drivers. The silence upon operation of the flexible drive cable is now-a-days one of the most important requirements to be fulfilled, and moreover the silence should be maintained and ensured for a long period of time.
In order to reduce the aforesaid noise and oscillation, many proposals have been made heretofore.
For example, U.S. Pat. No. 3,581,523, issued June 1, 1971 to D. D. Bartholomew, disclosed the construction to minimize the operational noise without employing lubricant, in which the liner member comprises an annular support section and a plurality of longitudinally extending resilient deformable ribs which are circumferentially spaced and adopted to resist radial movement of the core member upon rotation thereof.
U.S. Pat. No. 3,481,156 issued Dec. 2, 1969 to V. R. de Csipkes was also proposed. Although this invention is directed toward the flexible drive cable provided with longitudinal grooves which permit assembly of the cable by insertion of the core member into the passage of the liner member so that the corners of squared end of the core shaft pass through the passage via the grooves, mentions that the close radial clearance between the core member and the liner member is quite useful to abate the operational noise level. Nevertheless, these efforts which have been devoted to reduce the operational noise or oscillations, none of flexible drive cables hitherto known can fully fulfill aforesaid requirements. The inventor of this invention found that it should be provided with further three provisions or means below described to obtain a satisfied flexible drive cable.
First; a suitable soundproofing means to preclude the noise or oscillation produced upon engagement of a rotating core member against the inner face of the liner member from being transferred to the outer member and being propagated outside through the outer member.
Second; a means for well lubricating the interior of the liner member through the whole length thereof and for eliminating the abrasion to perform a silent operation for a long period of time. For that purpose, it should be noted that the flexible drive cable usually employs some types of liner member to guide and constrain an internally mounted rotatable shaft or core member which comprises generally more than two coils closely wound one on the other in alternately opposite directions. For such a construction stated above, a screw of a kind, i.e. coil-screw is fabricated at the exterior of the outermost coil with each wire wrapped therein. Therefore, in rotation of the core member, a lubricant which is essential to abate the abrasion of the liner member and filled between the core member and the liner member, is transferred in one direction along the passage of the liner member owing to the screw effect of the coil-screw, and the lubricant comes to show uneven distribution in volume along the passage.
The uneven distribution does not make good use of lubricant, and also it tends to wear the interior face of the liner member to result in increase of operational noise and shortening the life thereof.
Therefore, it is quite essential to preclude the transfer of the lubricant, and besides, it is to be noted that it is aggravated in accordance with the increase of the revolutional speed thereof.
Third; the means for reducing the operational noise per se is also to be provided to satisfy the aforesaid requirements.
The flexible drive cable in which the above three means are provided has never been obtained.
As for the second problem concerning the transfer of the lubricant, aforesaid U.S. Pat. No. 3,481,156 and U.S. Pat. No. 3,922,882 teach the usage of the liner member which has an inner face formed with longitudinal grooves or corner portions for residence of a lubricant to well lubricate the core member.
It is conceded that these structures have effect to lubrication of the core member, but it has been ascertained by the present inventor of the invention that the aforesaid transfer of lubricant can not be prevented sufficiently by structures stated in the aforesaid U.S. Patents.